This is a congenital foot deformity where there are two or more tarsal bones that have fused together or have failed to separate during fetal development.
Probably present at birth, but symptoms are rare in childhood due to flexible cartilage surrounding ossification centres
If movements at the subtalar joint are congenitally blocked by tarsal coalition, then the ankle joint remodels into a ball-and-socket joint to allow inversion and eversion.
- Calcaneonavicular coalition
- Talocalcaneal (Subtalar) coalition
It leads to a painful stiff foot during early adolescence. It often presents with recurrent ankle sprain and a rigid flatfoot. In children aged 8-14 there may be progressive lateral ankle pain and a mildly stiff hindfoot.
Most patients have a fixed hindfoot valgus. There is limited subtalar movement, which is worse in talocalcaneal coalition. There is a loss of the longitudinal arch. With tiptoe standing the arch does not reconstitute.
Plain films demonstrate calcaneonavicular coalition. X-ray is less likely to demonstrate talocalcaneal coalition, where it is usually the middle facet, and so CT is the gold standard imaging method.
- Activity modification
- Footwear adjustment
- Surgery if unsuccessful